Our overall objective is to understand the route by which a murine leukemia virus spreads through tissues of a mouse, whether this spread involves expression of or interaction with latent xenotropic viral information and how this spread changes under conditions which change the incidence of leukemia. This objective includes the analysis and comparison of two previously described variants of a leukemia virus which differ in the speed with which they cause leukemia. We will prepare virus-specific nucleic acid reagents by recombinant DNA techniques and use these reagents to measure the appearance of virus-specific nucleic acids in cells of infected mice.